The invention relates to a process for engraving a pattern into the surface of a work piece.
A device and a process for contact-free engraving by means of a laser is known from the patent document U.S. Pat. No. 4,156,124. A laser beam is, by means of a mask apparatus, directed onto the surface of a work piece. The said mask may be either transparent or reflective. The laser beam is transmitted by means of an optical device, and the image of the mask is thus cast onto the surface of the work piece. The mask and the work piece are held in parallel to one another at a fixed distance and position. The source of the laser beam is moved relative to the mask and the work piece surface, so that the laser beam migrates over the mask and, as a result, the surface of the work piece. By means of the mask, the intensity of the laser beam is changed in a manner which is dependent upon location and, consequently, the effect of the laser beam on the surface into which the pattern thus presented through the mask is engraved, as well. Only simple and rough patterns can be engraved by means of such a process and such an apparatus. In addition, the production of the masks is complicated and expensive. The masks are limited, so that only limited patterns can also only be engraved.
A device for the engraving of different types of letterings into a surface is known from the patent document U.S. Pat. No. 4,734,558. The ray coming from the laser is expanded to a parallel beam, which proceeds through a mask which can be controlled in a manner specific for location, and which mask acts as a screen, and corresponds to the lettering which is to be engraved. The image of the mask is cast onto the surface which is to be engraved. The mask is a light valve in the form of a liquid crystal, the permeability of which is controlled, in a manner dependent on location, by an image which is cast by the screen of a cathode ray tube onto the liquid crystal. The image on the cathode ray tube, which corresponds to the character which is to be engraved, is supplied by a microcomputer. Several stored memories to be engraved, which can be selected by means of switches which can be activated by hand, are stored in the memory in this microcomputer.
In this known device, therefore, metallic masks are replaced by an optical mask which is controlled by means of a mask generator. The characters which are to be engraved are of a simple nature, and must first be stored in memory in the mask generator by means of a special program.
A process which is essentially similar to the type which has just been described, in which the mask is likewise variable, is already known from the patent document DE 42 13 106 A1. The variation is brought about by means of a different digital control. The engraving is carried out in successive layers, one after the other. The numerical control of the mask permits only simple mask images, and thereby simple engraving patterns as well. The numerical control is brought about, for example, by means of one or several rotating aperture disks, the aperture images of which come to cover a specific configuration. The patterns are thus always regular. Small image elements are thus assembled into larger image fields in which, because of their regularity, they make a seamless transition into one another. Irregular patterns, such an assembly of image elements into larger image fields, is not possible without the appearance of visible boundary lines.
A process is the type which is stated in the introductory portion of claim 1 is known from the patent document U.S. Pat. No. 4,629,858, in which a pattern on a sheet of paper is scanned by line by line and the intensity of a laser is controlled by the scanned signal, and is, in the same manner, directed line by line over a work piece in the shape of a carpet, so that a deep pattern which corresponds to the pattern of color on the paper pattern is burned into the surface of the same. The design pattern thereby has a size which corresponds to the size of the work piece. The processing of a work piece which has a surface which is larger than that of the design pattern is thus not possible.
A process is known, from the patent document U.S. Pat. No. 3,739,088, which operates in accordance with the same principle as the process which has been stated above, and which is used for the production of printing plates. Here, too, the surface of the design pattern obviously corresponds to the surface of the printing plate which is to be produced.
The task which forms the basis of the invention is that of describing a process of the type for engraving a structure into the surface of a work piece by means of a laser beam which is directed onto the surface and controlled in its intensity in a location-dependent manner in dependence on the structure, which can be carried out in a simple manner and is also suitable for complicated and, in particular, irregular patterns and by means of which a surface on the work piece, which is larger than that of the design pattern, can be engraved.
The task which forms the basis of the invention is solved by means of the concept of storing depth contour information which is obtained from the surface sample in memory and the depth contour information which is stored in memory is recalled at least two times and at least two surface areas which adjoin one another on a boundary line are thereby engraved on the work piece.
The basic concept of the theory in accordance with the invention consists of the fact that the surface information which is obtained from the design pattern is stored in memory and is recalled at least two times, and at least two surface areas on the work piece which adjoin one another on a boundary line are thereby engraved. The surface area on the work piece which is scanned by the design pattern can thereby be doubled or multiplied as desired. It is thus not in one direction only that several patterns, which each correspond to the surface area which is being scanned, engage into one another in series, but also in two directions, so that the total surface which is engraved is correspondingly enlarged. If the pattern which has been scanned in the surface area of the design pattern is simple and/or if the boundaries of the surface area are selected favorably, then a boundary line does not appear between two surface areas which adjoin one another on the work piece. If the patterns do not insert into one another without a transition and in an invisible manner at a boundary line between two surface areas which adjoin one another, then, in accordance with one suitable further development of the invention, it is advantageous if the surface information which is stored in memory is, upon the second recall, read backwards and, if applicable, during further recalls, it is read alternately forward and backwards, in such a manner that, during the engraving, a mirroring of the sample is carried out at the boundary line or the boundary lines.
In all cases in which the surface information corresponding to the surface area of a design pattern is recalled at least two times, it is suitable for the surface information to be processed into the information areas which are adjacent to the boundary line or to the boundary lines between the surface areas on the work piece, in such a manner that a transition which is continuous and as invisible as possible for the human eye, is produced in the area of the boundary line. This processing can essentially be carried out in any manner, such as, for example, controlled by an operating person under visual control, which can be simply a handicraft process. One particularly suitable form of implementation of the processing consists of the fact, however, that the surface areas which correspond to the scanning surface area of the design pattern on the work piece are, by means of a corresponding recall of the surface information, preferably overlapping in time, which is stored in memory, brought to overlap on the boundary line or on the boundary lines, and that, the control signals in this area of overlap are continuously reciprocally lowered or raised, in such a manner that an essentially continuous and invisible transition of the pattern is formed over the boundary line. This means, in other words, that a cross-fading of the patterns is brought about in the area of the boundary line or of the boundary lines.
One other manner of implementation of the process, in accordance with the invention, for obtaining an invisible transition between adjacent engraved surface areas on the work piece in a manner which is similar to the form of implementation which has been stated above consists of the fact that the control signals for the laser beam are continuously attenuated or increased again in a transition area, adjoining with the boundary line, on both sides of the boundary line, whereby transition control signals are added to the control signals in the transition area, which are derived from the surface of the information of the design pattern, and then reversed as the control signals in the transition area are continuously raised and lowered again, in such a manner that an essentially continuous, invisible transition of the pattern is formed over the boundary line.
A natural pattern, particularly the grain of a natural leather pattern, can suitably be used as the design pattern. The work piece may be an embossing roller, particularly one for the continuous embossing of a sheet of thermoplastic foil. The forms of the process, which bring about a boundary-free transition of the pattern on a boundary line can, with particular advantage, be used for this process. An embossing pattern which is continuous over the circumference of the embossing pattern can thus be produced. If the embossing is supposed to take place in dependence on a natural design pattern, such as, for example, the grain pattern of a natural leather pattern, then the embossing surface must be a negative of the natural design pattern. In order to attain this, it is suitable, in accordance with one form of implementation of this further embodiment of the invention, to invert the control signals for the laser beam.